This application claims the priority of German application No 101 08 373.4, filed Feb. 21, 2001, the disclosure of which is expressly incorporated by reference herein.
This invention relates to an electric toothbrush and, more particularly, this invention relates to an electric toothbrush with a toothbrush shaft rotating in a brush casing and a bristle carrier disc which are connected to each other by a gear that converts the one-way rotary motion of the toothbrush shaft into a reciprocating rotary motion of the bristle carrier disc, and wherein the toothbrush shaft has at its end lying towards the rotatably mounted bristle carrier disc an eccentric which engages in a gap in the bristle carrier disc bounded by two bearing surfaces.
Such a toothbrush is known from WO 96/37164. The gap is formed by a slot in the bristle carrier disc, and the eccentric is formed by a double crank at the end of the toothbrush shaft. The free end of the crank must be aligned with the center of the bristle carrier disc in order for the eccentric to operate without play in the slot in all angular positions. To obtain adequate resistance to wear and the requisite absence of play and at the same time low friction in the known toothbrush, it is necessary that the toothbrush shaft be formed as a metal part, which greatly increases the cost of manufacture of the electric toothbrush.
The fundamental problem of the invention is to design an electric toothbrush of the kind stated at the outset so that all, or as nearly as possible all, of its parts can be produced as injection molded parts.
In accordance with the invention this problem is solved by forming the eccentric as a cam disc which is arranged on the toothbrush shaft and bridges the gap in every angular position.
This configuration enables the toothbrush shaft and cam disc to be formed as simple injection molded parts, or even to be combined as one injection molding. It means that sufficient absence of play can be achieved with standard manufacturing accuracies as the cam disc (disregarding its necessary eccentricity) does not need to be aligned with the center of the bristle carrier disc. Furthermore, if the toothbrush shaft and the cam disc are made as two parts, different angles of sweep of the bristle carrier disc can be obtained by fitting different cam discs.
In one embodiment that is especially advantageous, the cam disc has a surrounding helical groove which extends obliquely with respect to the cam disc, and the groove bottom forms the eccentric and bridges the gap between the two follower pins. This configuration results in, not point contact but line contact between the follower pins and the cam disc, and hence in a considerable reduction in wear.
In the embodiments which have so far been described, a cam disc engages in a slot in the bristle carrier disc on one side of the axis of rotation of the bristle carrier disc. A symmetrical and therefore torsionless application of force can be obtained if the bristle carrier disc has gaps disposed symmetrically and diametrically with respect to its axis of rotation and the toothbrush shaft accordingly has two cam discs oriented in opposite directions and each engaging in one of the gaps. The result is a quieter oscillating action of the bristle carrier disc. Furthermore, axially directed forces on the toothbrush shaft are avoided.
In one particularly simple construction of the electric toothbrush, the bristle carrier disc is rotatably seated in the barrel by its lateral cylindrical face and the toothbrush shaft passes underneath the bristle carrier disc to a bearing in the brush head on the same side as the free end of the brush casing. Such an embodiment can be manufactured at much lower cost than the embodiments which have so far been described.
The invention also makes it possible to impart different motions to different sets of bristles in the brush part, by rotatably mounting, concentrically within the bristle carrier disc, a further bristle carrier disc which likewise has an extension with opposing gaps in each of which, in a similar fashion to the cam discs for the outer bristle carrier disc, a cam disc of the toothbrush shaft engages, so that the toothbrush shaft has four cam discs altogether.
In a particularly simple embodiment, the two bearing surfaces extend parallel with each other and bear against the eccentric, and the eccentric is formed as a non-circular, approximately elliptical cam disc. The effect of this configuration is to compensate for the variation in the distance between the two bearing surfaces (viewed in projection) in the course of the reciprocating motion.
The toothbrush will operate with particularly low levels of play and friction if the bearing surfaces present a convex curvature to the lateral face of the eccentric. This ensures that the bearing surface extends tangentially to the lateral face of the cam disc at all times.
In a further configuration of the inventive toothbrush, the two bearing surfaces extend parallel with each other and bear against the eccentric and in the eccentric is formed as a non-circular, approximately elliptical cam disc.
In another embodiment, the bearing surfaces present a convex curvature to the lateral face of the cam disc.
In still another embodiment, the gap is formed between two follower pins projecting from a lower end face of the bristle carrier disc and the bearing surfaces are provided on these follower pins.
In yet another embodiment, close to its cam disc the toothbrush shaft has a rotating collar which fits into a bearing shell in the brush casing.
In a further embodiment, a section of the brush casing is formed by a lid which is removably inserted in an opening in the brush casing and forms part of the bearing shell.
In another configuration of the inventive toothbrush, the lid also forms a section of a holder for the bristle carrier disc.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.